Die casting method

ABSTRACT

A method of die casting parts with high temperature melting point metals and die casts parts in the form of turbine blades and ball valves. The die casting is done in a die element set having mold cavity and runner at parting surfaces and an injection cylinder opening its full bore diameter onto the parting surfaces. The mold cavity is preheated to a temperature of between 800*F. and 1,200*F., a casting temperature of about 3,000*F. is employed, and the injection plunger develops a casting pressure of between 8,000 psi and 12,000 psi.

United States Patent 1191 Cross [11] 3,810,505 [451' May 14, 1974 1 1 DIE CASTING METHOD [76] Inventor: Raymond B. Cross, 910 Greenbay Rd., Lake Forest, Ill. 60045 [22] Filed: Oct. 17, 1972 [21] Appl. No.: 298,409

Related (1.5. Application Data [52] US. Cl 164/113, 164/120, 164/304 [51] Int. Cl 322d 13/00, B22d 27/10 [58] Field of Search 164/120, 113,303, 304, 164/315 [56] I References Cited UNITED STATES PATENTS Rl8,202 9/1931 Polak 164/313 3,443,628 5/1969 Carr 164/313 3,106,002 10/1963 Bauer I 164/120 3,533,464 10/1970 Parlanti e! 211.. I. 164/312 3,615,880 10/1971 Barto et a1. 164/113 3,528,478 9/1970 Koch et a1. 164/113 FOREIGN PATENTS OR APPLICATIONS 128,049 10/1928 Switzerland 164/313 536,671 10/1931 Germany 164/120 OTHER PUBLICATIONS Experience in Pressure Die Castinglof Steel 1 In the USSR, Josef Sebl, [Translated from Slvz'irenstvi' [Czechoslovakia V01. 8, 1960, No. 9, 33l332 1962 by Henry Brutcher Machinery" Vol. 42, No. 6, pp. 361366, February 1936, by Chas. 0. Herb Recent Die Casting Developments by Sam Tour and F. .1. Tobias, The Foundry, February 1934, pp. 2 l23, 62 (see especially p. 23, FIG. 2)

Primary E.\'aminer,1, Spencer Overholser Assistant ExaminerV, K. Rising Attorney, Agent, or Firm-Richard G. Lione I ABSTRACT 3,000F. is employed, and the injection plunger develops a casting pressure of between 8,000 psi and 12,000 psi. r

4 Claims, 5 Drawing Figures DIE CASTING METHOD This application is a continuation-impart of copending application Ser. No. 95,440, filed Dec. 7, 1970. Reference is also made to application Ser. No. 865,397, filed Oct. 10, I969, now US. Pat. No. 3,646,990, issued Mar. 7, 1972, from which the aforementioned co-pending application Ser. No. 95,440 is a division. Further reference is made to application Ser. No. 769,598, filed Oct. 22, 1968, now abandoned, from which the aforementioned application Ser. No. 865,397 is a continuation-in-part.

FIELD OF THE INVENTION This invention relates in general to die casting. It deals particularly with a method and apparatus for die casting high temperature melting point metals, as well as the die cast products of the method.

BACKGROUND OF THE INVENTION As pointed out in the aforementioned applications, one critical facet of a die casting operation, regardless of the metal being cast, is the injection of molten metal into the mold. It is especially critical where high temperature melting point metals are bieng cast. In this respect, the melting point of copper is 198 l .4" F. and that of iron 2,797F., while some brasses melt at approximately 2,400F. Ferrousalloys'melt at temperatures of 3,000F. and higher. Any metals in the melting point range of approximately 2,000F., are, for purposes of this disclosure, considered high temperature melting point metals.

Conventional methods employing hot chamber or cold chamber machines have generally been inadequate, or barely adequate, to the test of die casting with such high temperature melting point metals. As a result, little die casting of these metals was done prior to the development of the methods and apparatus disclosed in the aforementioned patent applications. New die casting injection systems, die arrangements and methods which product excellent die castings with high temperature melting point metals are disclosed in these applications. As the system, die arrangements and methods have been employed since their conception, improvements have evolved in equipment, methodology and products.

SUMMARY OF THE INVENTION A primary object of the present invention is to provide an improved method of die casting with high temperature melting point metals such as the iron and copper alloys, for example. Another object is to provide an improved method of die casting parts having either thin sections or relatively thick sections from metals having high temperatures melting points. Still another object is to provide an improved method of the aforedescribed character which produces parts having desired metallurgical properties, including relatively small, uniform grain structure. Yet another object is to provide a method of die casting turbine blades for gas turbine engines and the like from high temperature melting point metals such as a high alloy steel. A further object is to provide a method of die casting ball valves from high alloy steel. A further object is to provide improved turbine blade and ball valve products from the method of the invention.

The foregoing and other objects are realized in accord with the invention by providing a method of die casting, and the product of such method, wherein parts having desired physical characteristics are produced from high temperature melting point metals. More specifically, high quality turbine blades for gas turbine engines and ball valves for fluid control systems have been die cast from stainless steel using the basic methods and apparatus described in the aforementioned patent applications together with newly developed methodology involving casting temperatures. pressures and mold pre-heat temperatures.

The method contemplates utilization of a die arrangement of the type described and claimed in the aforementioned US. Pat. No. 3,646,990. Such a die arrangement provides an injection cylinderopening its fullbore diameter onto the parting line of the die elements which enclose the die cavity. The casting runner from the injection cylinder to the die cavity is also at the parting line. The injection cylinder is filled with a predetermined amount (shot) of molten metal which uniformly contacts the injection cylinder wall along the axial length of the shot in the cylinder.

According to the method improvement of the present invention, the molten metal is poured at a temperature precalculated to place it at a temperature slightly above its freezing temperature when the shot has been completely introduced to the injection cylinder. With No. 4lOSS stainless steel, which is used according to the invention in casting turbine blades, and with No. 304SS stainless steel, which is used in casting ball valves, that temperature is 3,000F. When the molten metal is melted in a furnace separate from the casting machine and carried by hand or automated ladling to the machine, a superheat of F. is added to the melt to compensate for heat losses during pouring.

In the meantime, the die cavity itself is preheated to between 800l,200F. Preferably, the preheating of the die cavity is done with heating elements buried in the die cavity insert itself. The die cavity insert itself may be fabricated of an alloy steel, or it has been found that Anvilloy, a tungsten-based alloy manufactured by the Mallory Corporation, makes a suitable die cavity insert material.

According to the invention, the shot cylinder of the machine has a diameter of from 1% to 2 inches and, accordingly, the shot tip of the injection plunger is approximately the same diameter. When it is actuated by hydraulic pressure, the injection plunger moves three inches in 0.25 seconds to develop a casting pressure of 8,000 to 12,000 psi in the die cavity. After injection of the molten high temperature melting point metal, the plunger remains actuated. A chill time of 2 seconds is permitted before the dies are separated, although actual freezing of the casting occurs in substantially less than 2 seconds. As the dies are separated, the casting is knocked out and all remaining scrap removed at the parting line. The plunger is then retracted.

The castings which have been produced according to the present invention are stainless steel turbine blades and ball valves of conventional configuration. In both instances, the finished part has been found to have a fine, uniform grain structure. Excellent physical strength and surface finish result.

BRIEF DESCRIPTION OF THE DRAWING The invention, both as to the construction of a machine with which the method may be practiced, the method of invention itself, and the products of the invention, is illustrated more or less diagrammatically in the drawing, in which:

FIG. 1 is a perspective view of a portion of a die arrangement and molten metal feed mechanism with which the method of the invention may be practiced;

FIG. 2 is a sectional view taken through mated die elements in a die arrangement of the type shown in FIG. 1;

FIG. 3 is a perspective view of the die inserts used in the die arrangement and molten metal feed mechanism .shown in FIGS. 1 and 2;

FIG. 4 is a perspective view of a turbine blade die cast according to the invention; and

FIG. 5 is a perspective view ofa ball valve die cast according to the invention. I

DESCRIPTION OF THE PREFERRED EMBODIMENTS cludes a fixed die element 11 and a movable die element 12 which meet and mate on a parting line P at op posed planar faces 13 and 14, respectively, to form mold cavities 15 or mold insert cavities, in both faces in the present example. The insert cavities 15 are, in the present illustration, adapted to receive mold inserts 16 (see FIG. 3) having mold cavity segments 17 which function in a manner hereinafter discussed.

,The fixed die element 11 is mounted in a generally conventional manner on a fixed platen (not shown) 'of adie casting machine while the movable die element 12 is, correspondingly, mounted in a generally conventional manner on its movable platen (not shown). The movable die element 12 is, in this manner, movable lntersecting the sprue and runner complex at the juncture of the sprue 25 and the runner 26 is the injection cylinder 30. The injection cylinder 30 extends perpendicularly to the sprue and runner complex, through the fixed die elements ll (and platen), from the back of the platen to its inner end 32 where it opens into the sprue complex 20 at the juncture of the sprue 25 and the runner 26.

In practice, the injection cylinder 30 is actually defined by a sleeve (not shown) fabricated of a high strength, high temperature resistant metal alloy. For ease of description and explanation of theinvention, however, the sleeve is not illustrated.

Slideable in the cylinder 30, in close fitting relationship with the sleeve, is an injection plunger 38. As will be recognized, the full diameter of the sleeve opens onto the parting line P at its inner end 32. According to the present invention, the diameter of the sleeve is between 1%: and 2 inches, l% inches in the present illustration. The diameter of the injection plunger 38 is approximately one sixty-fourth of an inch less or I and fourty seven sixty-fourths inches in diameter so that it slides freely but snugly in the cylinder 30.

The injection plunger 38 is inserted from the open rear end of the cylinder 30 behind the platen and is slideable toward the front end 32 of the cylinder. The tip 39 of the plunger 38 forces molten metal upwardly through the'runner 26 into the mold cavity to form the casting, in a manner hereinafter discussed.

Also intersecting the sprue complex 20, at a point above the level of the cylinder 30, is a sprue locking cylinder 40. The sprue locking cylinder 40 extends perpendicular to the sprue complex 20, through the die element 11 (and platen) from the back of the platen through the sprue 21 to its inner end 42 in the die element 12. Once again, the cylinder 40 is actually defined by a sleeve, or segmented sleeve which extends through and is mounted in suitably formed bores in the die elements 11 and 12, but is not shown for reasons already made clear.

A sprue plunger 45 is slideable in the locking cylinder 40 from the rear end of the cylinder into a position into and out of engagement with the fixed die element 11 in a well-known manner. I

The 'die arrangement and molten metal. feed mechanism 10 also includes a sprue and runner complex 20- through which molten metal is delivered to the mold cavity definedby the mated segmentsl7. The complex 20 includes an inclined pouring sprue 21 having a pouring spout 22 at its upper end opening to the top of the die element 11. A horizontal sprue 25 joins the lower end of the pouring sprue 21 to a vertically disposed casting runner 26 through an injection cylinder 30. The runner 26'communicates with the mold cavity.

The sprue complex 20, including the sprues 21, 25 and the runner 26, is formed entirely at the parting line P of the mating die elements 11 and 12. In the die arrangement and feed mechanism 10, the sprues 21, 25 and the runner 26 are formed in the face 13 ofthe fixed die element 11. With the die elements 11 and 12 in mating relationship, the sprues and runner are closed.

where it extends across the sprue 21 into the die element 12 and forms a liquid lock in the sprue 21. An ejection plunger 46 slideable in the sprue locking cylinder 40 section which is formed in the die element 12, is effective to kick out the hardened sprue scrap from this section of the cylinder.

The injection plunger 38, the sprue plunger 45 and the ejection plunger 46 are each operated through their mounting platens by suitable hydraulic motor means not shown). In the case of the injection plunger 38, according to the described embodiment of the invention, a hydraulic cylinder having a 5 /2 inch diameter is employed. The cylinder develops 1,000 psi fluid pressure, effective to move the injection cylinder 38 from its retracted position, as illustrated in FIG. 2, into an actuated position in which it has forced molten metal into the die cavity.

In operation of the die arrangement and molten metal feed mechanism 10, the plungers 38 and'45 are initially held in retracted positions in the injection cylinder 30 and lockingcylinder 40, respectively. Similarly, the ejection plunger 46 is positioned as illustrated in FIG. 2. According to the method of the invention, molten number 41055 (stainless steel), for example, in

the case of the turbine blade casting, is poured into the pouring spout 22, through the sprue 21, across the horizontal sprue 2S, and into the injection cylinder cylinder 30 between the tip 39 of the plunger 38 and the front end 32 of the cylinder. Sufficient molten metal is introduced to fill the cylinder 30 and the sprue 25, as well as some portion of the inwardly inclined sprue 21 and the runner 26. All air has thus been evacuated from the injection cylinder 30 and the molten metal is in contact with the cylinder sleeve around its entire circumference along the axial length of the metal shot.

The molten 410SS (stainless steel) is poured into the pouring sprue at a temperature of approximately 50F. above its freezing temperature or, in the case of this alloy, 3,000F. In the illustrated die casting machine, the alloy is melted in a separate furnace adjacent the machine and then hand-ladled into the sprue 21. To compensate for heat losses during the handling of the molten metal, the metal in the furnace is heated to 3,150F., or a 150F. superheat.

Immediately after the molten metal has been poured into the injection cylinder 30, the sprue plunger 45 is moved inwardly to its actuated position to lock or block-off the sprue 21 and prevent molten metal from backing up the sprue when the injection plunger 38 is actuated. At this point, the injection plunger 38 is forced inwardly to its actuated position in the cylinder 30, forcing molten metal through the runner 36 into the mold cavity.

The mold insert cavity in each of the die elements 11 and 12 has a mold insert 16 seated therein, as has been pointed out. The mold inserts 16 are roughly mirror images of each other and comprise blocks of high alloy steel or the aforementioned tungsten-based alloy, Anvilloy, for example. Each insert 16 has a die cavity segment .17 for a turbine blade TB (see FIG. 4) formed in its die face 51. In addition, a runner extension 260 connects at least one of the die cavity segments 17 in the insert 16 with the runner 26 when the die insert is seated.

Each die insert 16 has apair of electrical resistance heating rods extending vertically through it in transversely spaced relationship immediately behind the corresponding die cavity segment 17. With the die inserts 16 seated in cavities 16, these electrical resistance heating rods 55 are connected to a conventional source of electric power. Before the molten metal injection cycle is started at the outset ofa casting sequence, the die inserts 16 are heated by means of these rods to a temperature of 800?. The aforedescribed molten metal charging cycle is then initiated.

The casting fill time, according. to the method of the present invention, is 0.25 seconds. In other words, the injection plunger 38 moves its full travel, three inches in the present illustration, in 0.25 seconds to completely fill the die cavity formed by the segments 17 in 0.25 seconds. A casting pressure of between 8,000 and 12,000 psi is developed, also according to the method of the invention.

The injection plunger 38 remains in its actuated position as the turbine blade TB freezes. A freeze or chill time of two seconds is permitted before the casting mechanism is actuated to separate the die elements 11 and 12. After separation ofthe die elements 11 and 12, the ejector plunger 46 is actuated together with conventional ejector pins (not shown) in the die element 12 and the cast blade TB with the runner and gate scrap attached is kicked out of the mold.

As the die casting machine is repeatedly cycled to produce turbine blades, the temperature of the die inserts 16 has a tendency to rise. Obviously, not as much heating by the resistance heating elements 55 is required. It is critical to the invention that the temperature not be permitted to rise above l,200F.

With a preheat of the die inserts to a temperature of 800l-,200F. and a casting pressure of 8,000 to 12,000 psi, turbine blades TB having excellent mechanicalproperties are cast. A uniform, fine grain structure results. If the die insert temperature slips below 800F., a rather poor surface results; while if it exceeds l,200F., there is poor solidification and a coarse grain structure results. In either case, the turbine blade TB must be scrapped.

FIG. 5 illustrates a ball valve BV cast from 30488 stainless steel according to the method of the invention. A uniform, fine grain structure results. The die temperatures and casting pressures and temperatures remain the same. The method is substantially identical.

The method of the invention has, to date, been discussed solely in terms of pouring molten metal into the injection cylinder 30. In an alternative form preparing the melt, however, the present invention contemplates induction melting right in the cylinder 30. FIG. 2 shows induction heating coils encircling the cylinder 30.

In the induction coil 80melting method, a slug of metal is introduced to the cylinder 30 and then the plunger 38 inserted. A melt takes about thirty seconds. Because the entire cylinder 30 is heated to melt temperature it doesnt deform non-uniformly. The method then proceeds as previously described.

While several embodiments described herein are at present considered to be preferred, it is understood that various modifications and improvements may be made therein.

What is desired to be claimed and secured by Letters Patent of the United States is:

l. A method of die casting steel to produce a part having a uniform, fine grain structure and excellent physical characteristics and surface finish, comprising the steps of:

a. providing mating die elements which separate at parting surfaces wherein a molten metal pouring sprue, runner and mold cavity areeach disposed at parting surfaces and wherein a cylinder extends through at least one of said die elements into communication at said parting surfaces with said sprue and said runner,

b. closing said die elements into mated relationship,

c. positioning a plunger in said cylinder,

d establishing a mold cavity surface temperature of between 800 and l,200 F.,

e. introducing molten steel at a temperature of approximately 50F above its freezing temperature to said sprue and permitting it to flow unchecked into said cylinder to fill said cylinder at least to the point where said sprue enters the cylinder without any molten metal flowing into the mold cavity,

f. causing said sprue to be blocked so that molten metal cannot flow back through said sprue,

g. moving an injection plunger through said injection cylinder from a retracted position to an actuated position to force molten metal through said runner into said mold cavity until said mold cavity is filled and generating a casting pressure of at least 8,000 psi, and

h. separating the die elements after the metal has hardened to remove the casting and the gate at parting surfaces.

2. The method of claim 1 further characterized by and including the step of: 1

a. generating a casting pressure of between 8,000 psi and 12,000 psi on the molten metal in said mold cavity.

3. A method of die casting steel to produce a part having a uniform, fine grain structure and excellent physical characteristics and surface finish. comprising the steps of: y 1

a. providing mating die elements which separate at parting surfaces wherein a molten metal pouring sprue, runner and mold cavity are each disposed at parting surfaces and wherein a separate cylinder extends through at leastone of said die elements into communication at said parting surfaces with said sprue and said runner,

b. closing said die elements into mated relationship,

c. positioning a plunger in said cylinder so that access to said cylinder for introduction of molten metalthereto is afforded only through said sprue, d. establishing a mold cavity surface temperature of between'800 F. and l,200 F.,

e. introducing molten steel at a temperature of approximately 50F above its freezing temperature to said sprue and permitting it to flow unchecked into said cylinder to fill said cylinder at least to the point where said sprue enters the cylinder without any molten metal flowing into the mold cavity,

f. causing said sprue to be blocked so that molten metal cannot flow back through said sprue,

g. moving an injection plunger through said injection cylinder from a retracted position to an actuated position to force molten metal through said runner into said mold cavity until said mold cavity is filled and generating a casting pressure of at least 8,000

psi, and

- h. separating the die elements after the metal has hardened to remove the casting and the gate at parting surfaces.

4. A method of die casting a relatively thin walled structure such as a turbine blade or the like to produce a casting having a uniform. fine grain structure, excel lent physical characteristics and surface finish from No. 41055 stainless steel, comprising the steps of:

a. providing mating die elements which separate at parting surfaces wherein a molten metal pouring sprue, runner and mold cavity are each disposed at parting surfaces and wherein a cylinder extends through at least one of said die elements into communication at said parting surfaces with said sprue and said runner,

b. closing said die elements into mated relationship,

C. positioning a plunger in said cylinder,

d. establishing a mold cavity surface temperature of between 800 F. and 1,200 F.,

e. introducing molten 410SS steel at a temperature of as close to 3,000 F. as possible to said sprue and permitting itjto flow unchecked into said cylinder to fill said cylinder at least to the point where said sprue enters the cylinder without any molten metal flowing into the mold cavity,

f. causing said sprue to be blocked so that molten metal cannot flow back through said sprue,

g.- moving an injection plunger through said injection cylinder from a retracted position to an actuated position to force molten metal through said runner into said mold cavity until said mold cavity is filled and generating a casting pressure of at least 8,000 psi, and 7 h. separating the die elements after the metal has hardened to remove the casting and the gate at parting surfaces. 

1. A method of die casting steel to produce a part having a uniform, fine grain structure and excellent physical characteristics and surface finish, comprising the steps of: a. providing mating die elements which separate at parting surfaces wherein a molten metal pouring sprue, runner and mold cavity are each disposed at parting surfaces and wherein a cylinder extends through at least one of said die elements into communication at said parting surfaces with said sprue and said runner, b. closing said die elements into mated relationship, c. positioning a plunger in said cylinder, d. establishing a mold cavity surface temperature of between 800* and 1,200* F., e. introducing molten steel at a temperature of approximately 50*F above its freezing temperature to said sprue and permitting it to flow unchecked into said cylinder to fill said cylinder at least to the point where said sprue enters the cylinder without any molten metal flowing into the mold cavity, f. causing said sprue to be blocked so that molten metal cannot flow back through said sprue, g. moving an injection plunger through said injection cylinder from a retracted position to an actuated position to force molten metal through said runner into said mold cavity until said mold cavity is filled and generating a casting pressure of at least 8,000 psi, and h. separating the die elements after the metal has hardened to remove the casting and the gate at parting surfaces.
 2. The method of claim 1 further characterized by and including the step of: a. generating a casting pressure of between 8,000 psi and 12,000 psi on the molten metal in said mold cavity.
 3. A method of die casting steel to produce a part having a uniform, fine grain structure and excellent physical characteristics and surface finish, comprising the steps of: a. providing mating die elements which separate at parting surfaces wherein a molten metal pouring sprue, runner and mold cavity are each disposed at parting surfaces and wherein a separate cylinder extends through at least one of said die elements into communication at said parting surfaces with said sprue and said runner, b. closing said die elements into mated relationship, c. positioning a plunger in said cylinder so that access to said cylinder for introduction of molten metal thereto is afforded only through said sprue, d. establishing a mold cavity surface temperature of between 800* F. and 1,200* F., e. introducing molten steel at a temperature of approximately 50*F above its freezing temperature to said sprue and permitting it to flow unchecked into said cylinder to fill said cylinder at least to the point where said sprue enters the cylinder without any molten metal flowing into the mold cavity, f. causing said sprue to be blocked so that molten metal cannot flow back through said sprue, g. moving an injection plunger through said injection cylinder from a retracted position to an actuated position to force molten metal through said runner into said mold cavity until said mold cavity is filled and generating a casting pressure of at least 8,000 psi, and h. separating the die elements after the metal has hardened to remove the casting and the gate at parting surfaces.
 4. A method of die casting a relatively thin walled structure such as a turbine blade or the like to produce a casting having a uniform, fine grain structure, excellent physical characteristics and surface finish from No. 410SS stainless steel, comprising the steps of: a. providing mating die elements which separate at parting surfaces wherein a molten metal pouring sprue, runner and mold cavity are each disposed at parting surfaces and wherein a cylinder extends through at least one of said die elements into communication at said parting surfaces with said sprue and said runner, b. closing said die elements into mated relationship, c. positioning a plunger in said cylinder, d. establishing a mold cavity surface temperature of between 800* F. and 1,200* F., e. introducing molten 410SS steel at a temperature of as close to 3,000* F. as possible to said sprue and permitting it to flow unchecked into said cylinder to fill said cylinder at least to the point where said sprue enters the cylinder without any molten metal flowing into the mold cavity, f. causing said sprue to be blocked so that molten metal cannot flow back through said sprue, g. moving an injection plunger through said injection cylinder from a retracted position to an actuated position to force molten metal through said runner into said mold cavity until said mold cavity is filled and generating a casting pressure of at least 8,000 psi, and h. separating the die elements after the metal has hardened to remove the casting and the gate at parting surfaces. 